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M15 Q11

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M15 Q11 [#permalink] New post 24 Jul 2012, 19:50
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

33% (00:00) correct 67% (02:11) wrong based on 3 sessions
Is |x - y| \gt |x + y| ?

x^2 - y^2 = 9
x - y = 2

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
EACH statement ALONE is sufficient
Statements (1) and (2) TOGETHER are NOT sufficient

Statement (1) by itself is insufficient. S1 gives us information about (x - y)(x + y) but does not tell how (x - y) and (x + y) compare to each other.

Statement (2) by itself is insufficient. S2 gives no information about (x + y) .

Statements (1) and (2) combined are sufficient. From S1 and S2 it follows that 2(x + y) = 9 from where (x + y) = 4.5 . Now we can state that |x - y| = 2 \lt |x + y| = 4.5 .
The correct answer is C.

I can't get the right numbers to test statement 2 to prove it Insuff. Please help. All the numbers I tried have me NO. Please help.
[Reveal] Spoiler: OA
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Re: M15 Q11 [#permalink] New post 24 Jul 2012, 20:27
Expert's post
teal wrote:
Is |x - y| \gt |x + y| ?

x^2 - y^2 = 9
x - y = 2

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
EACH statement ALONE is sufficient
Statements (1) and (2) TOGETHER are NOT sufficient

Statement (1) by itself is insufficient. S1 gives us information about (x - y)(x + y) but does not tell how (x - y) and (x + y) compare to each other.

Statement (2) by itself is insufficient. S2 gives no information about (x + y) .

Statements (1) and (2) combined are sufficient. From S1 and S2 it follows that 2(x + y) = 9 from where (x + y) = 4.5 . Now we can state that |x - y| = 2 \lt |x + y| = 4.5 .
The correct answer is C.

I can't get the right numbers to test statement 2 to prove it Insuff. Please help. All the numbers I tried have me NO. Please help.


statement 1
x^2 - y^2 = 9
or, (x+y)(x-y)=9
Clearly not sufficient (different combinations of x+y and x-y are possible)

statement 2
x-y=2
not sufficient with no info on (x+y)

combining both together
x+y=9/2
x-y=2

so |x-y|<|x+y|
Sufficient
Hence C
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Re: M15 Q11 [#permalink] New post 24 Jul 2012, 23:02
can you please suggest some numbers to prove statement 2 insuff??
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Re: M15 Q11 [#permalink] New post 24 Jul 2012, 23:08
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Re: M15 Q11 [#permalink] New post 24 Jul 2012, 23:10
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Re: M15 Q11 [#permalink] New post 25 Jul 2012, 00:59
For statement 2, use these values to prove that the statement alone is insufficient.

x=2 and y=0
x=3 and y=1
x=-1 and y=-3

Always make a point to check for the inequality with 0 as a value.

Kind Regards,
Ravender
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Re: M15 Q11 [#permalink] New post 25 Jul 2012, 01:07
Expert's post
palsays wrote:
For statement 2, use these values to prove that the statement alone is insufficient.

x=2 and y=0
x=3 and y=1
x=-1 and y=-3

Always make a point to check for the inequality with 0 as a value.

Kind Regards,
Ravender


@palsays
I dont think your values provide insufficiency
for x=2, y=0 |x+y|>|x-y|
for x=3, y=1 |x+y|>|x-y|
for x=-1, y=-3 |x+y|>|x-y|

You have to make one variable negative and one variable postive to show that |x+y|<|x-y|
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Re: M15 Q11 [#permalink] New post 25 Jul 2012, 01:10
teal wrote:
Is |x - y| \gt |x + y| ?

x^2 - y^2 = 9
x - y = 2

Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
EACH statement ALONE is sufficient
Statements (1) and (2) TOGETHER are NOT sufficient

Statement (1) by itself is insufficient. S1 gives us information about (x - y)(x + y) but does not tell how (x - y) and (x + y) compare to each other.

Statement (2) by itself is insufficient. S2 gives no information about (x + y) .

Statements (1) and (2) combined are sufficient. From S1 and S2 it follows that 2(x + y) = 9 from where (x + y) = 4.5 . Now we can state that |x - y| = 2 \lt |x + y| = 4.5 .
The correct answer is C.

I can't get the right numbers to test statement 2 to prove it Insuff. Please help. All the numbers I tried have me NO. Please help.


In fact, the given inequality can be rewritten as (x-y)^2>(x+y)^2 - we can square both sides, as they are both positive. Rearranging the terms, the question becomes xy<0 (is the product xy negative)?

Then, it is much easier to understand that neither (1), nor (2) alone is sufficient.
Taking both statements, one can explicitly find the values of x and y (although not necessary), and check whether their product is negative.
That's why the correct answer should be C.
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Re: M15 Q11 [#permalink] New post 25 Jul 2012, 01:35
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Re: M15 Q11   [#permalink] 25 Jul 2012, 01:35
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